Slope-assisted complementary-correlation optical time-domain analysis of Brillouin dynamic gratings for high sensitivity, high spatial resolution, fast and distributed fiber strain sensing

The performance of an optical time-domain sensing technique, employing the slope of Brillouin dynamic gratings in polarization-maintaining fibers, can be significantly enhanced using Golay complementary sequences. The strain sensitivity of the reflectivity of a coded probe primarily depends on the detuning between the orthogonally polarized pumps, which generated the grating. The system broadband sensitivity for a 256 bit unipolar probe code was demonstrated to be 50n epsilon/root Hz at a sampling rate of 2MHz, which to the best of our knowledge is a record sensitivity for Brillouin dynamic sensing. We report the measurement of 10kHz strain vibrations (which is the bandwidth limit of the vibration source) with a spatial resolution of 2cm. Owing to the system high sensitivity and spatial resolution, it has the potential to be used in distributed ultrasonic detection applications.